In the past, oil shale deposits were mined and brought to the surface for further processing of the various components and constituents. This process was expensive, time-consuming, and dangerous. If the oil shale deposits were mined by open pit, their removal was time-consuming and expensive. Additional ecological problems render this method of extraction undesirable today.
A somewhat more dangerous approach involves underground tunneling into the shale oil deposits in a predetermined pattern for the purpose of blasting and rubblizing the oil shale deposit. After the deposit is rubblized, a flame front is instituted which causes an in-situ retorting of the hydrocarbon values in the shale. This process has met with varying success primarily because of difficulty of obtaining uniform rubble in the shale deposit with the attending problems of maintaining a reasonably uniform flame front and plastic flow of the rock material. If the rubble is not reasonably uniform, a substantially uniform flame front is not maintained and the retort flames are quenched by the retorting products, or by-pass burning occurs.